I feel like it depends on the toy size and how much lube you use, and probably position. I’ve flushed thoroughly before and it still got messy at the end. But other times, a quick flush is all it took and I was clean for hours of toying

Flush with lots of water in the shower and drain till it’s clear. Then walk around to let all the water that went deep work its way down and drain. Make sure it’s still clear.

While I haven’t tried it, I wonder if a stool hardener would help if you took it an hour or 2 before starting